To analyze any trace compounds, e.g., drugs, contained in a biological sample, such as blood and serum or the like, it is necessary to purify and concentrate the compounds, since the constituents to be assayed are in very small quantities.
One method often used to efficiently purify and concentrate compounds is automated solid-phase extraction, where an apparatus is desired that is more compact, capable of conducting a larger number of types of analyses, and higher in throughput. Solid-phase extraction is a method of separating, purifying, and concentrating an analyte (or a substance to be assayed), by retaining this substance in a solid phase extracting agent (e.g., a plurality of small beads or membrane-like substances) in packed form in a small container such as a minicolumn or cartridge, then washing the solid phase extracting agent, and collecting desired compounds from the solid phase extracting agent.
The step of collecting the desired compounds by the solid phase extraction includes five process steps: (1) a solid-phase extracting agent conditioning step in which to pass an organic solvent through the solid phase extracting agent, (2) a solid-phase equilibrating step in which to pass a water-based solvent through the solid phase extracting agent, (3) the step of retaining the analyte in the solid phase extracting agent by passing the sample through the solid phase extracting agent, (4) a washing step in which to pass water through the solid phase extracting agent, and (5) the step of passing the organic solvent through the solid phase extracting agent and eluting the analyte from the solid phase.
An example of an automatic solid-phase extraction apparatus is described in Patent Document 1, for example. The automatic solid-phase extraction apparatus described therein includes a vacuum rack equipped with a multiple solid-phase plate bank, a dispensing head that suctions and discharges a liquid, and means that transfers the dispensing head.
The above conventional extraction apparatus enables a batch-processing (using 96 holes plate) capability and an ability to purify and concentrate analyte constituents in blood, serum, and the like, automatically. The solution containing purified and concentrated analytes, thus obtained, are transferred to a liquid-chromatography or a mass spectrometry instrument for qualitative and quantitative analyses of the trace analyte substances, e.g., drugs, contained in the biological sample, such as blood and serum or the like.
This technique adopted in the conventional extraction apparatus is effective in that conventional manual pretreatment by the analyzing person prior to mass spectrometry has been automated, so as to accelerate significant reduction in time and in statistical variations in data.